We are attempting to develop enriched populations of antigen specific T cells in both the guinea pig and mouse in order to study the biochemical nature of the T cell receptor. The role of Ia H2D and H2K in T-cell mediated cytotoxicity will be studied. The biology and biochemistry of murine IgD will be investigated. Its structure on the cell surface will be studied after surface radioiodination. The site of binding of IgD to the plasma membrane will be explored by removing such immunoglobulin and allowing it to bind back to the surface of denuded B cells. The topography of surface alloantigens including H-2 and Thy-1 will be explored using scanning electron microscopy and hybrid antibody to the alloantigen in question and to a virus marker. The biochemistry of alloantigens will be further studied at the level of peptide mapping in order to explore structural homology and thereby to elucidate the evolution of the antigens in question as well as to understand structure function-relationships. The basis of tropism of leukemia viruses in the mouse will be explored. Within this framework, an attempt will be made to isolate receptors for such viruses on various purified populations of lymphocytes.